Activation of the Ras-GRF/CDC25(Mm) exchange factor by lysophosphatidic acid

The Ras-GRF exchange factor can activate Ras-dependent responses following the activation of heterotrimeric G-protein and calcium signalling. In stabl e lines of NIH-3T3 fibroblasts that express Ras-GRF, the agonist lysophosph atidic acid (LPA) increases the phosphorylation state and activity of Ras-G RF. The stimulation of Ras GRF can be demonstrated in vitro, in an assay us ing recombinant Ras substrate, and in situ, by a selective increase in the ability of LPA to stimulate mitogen activated protein (MAP) kinase. The inc rease in Ras-GRF phosphorylation state, which occurs on serine residues, an d the increase in exchange factor activity are blocked by pretreatment with pertussis toxin. Activation of Ras-GRF by LPA can also be inhibited by che lation of intracellular calcium and treatment of the Ras-GRF with protein p hosphatase 1 (PP1), supporting a model in which Ras GRF serves to integrate signals from multiple transduction pathways. CELL SIGNAL 11;8:603-610, 199 9. (C) 1999 Elsevier Science Inc.